Mantle Edge Research Articles

Identification of insulin-like peptides in cerebral ganglia neurosecretory cells of the mussel Mythus edulis

The immunostaining patterns of cerebral ganglia sections from the mussel Mytilus edulis with monoclonal antibodies raised against cerebral ganglia (CG) extracts were compared to those obtained with various polyclonal anti-insulin-like antibodies. One of the monoclonal antibodies (MAB 46) revealed clusters of positive cells in localization comparable to those revealed by the polyclonal antibodies. The nature of the antigen recognized by MAB 46 and the polyclonal antibodies was compared by gel filtration-HPLC of a cerebral ganglia extract. Similar peaks were revealed by the monoclonal and polyclonal antibodies. MAB 46 significantly inhibited the cerebral ganglia induced stimulation of amino-acid incorporation by mantle edge cell suspensions, suggesting that the antigen recognized by MAB 46 is involved in the control of growth.

Eyes as optical alarm systems in fan worms and ark clams

Eye structure and optics were investigated in two sabellid polychaetes (Sabella melanostigma, Dasychone conspersa) and three arcacean bivalves (Arca zebra, Barbatia cancellaria, Anadara notabilis). The polychaetes have numerous compound eyes arranged in pairs along the branchial tentacles. Each ommatidium is composed of three cells: one receptor cell forming a ciliary receptive segment, and two pigment cells forming an extracellular lens (crystalline cone). The ark clamsAreaandBarbatiapossess large numbers of compound eyes arranged along the mantle edge. The ommatidia of these eyes are composed of one or two ciliary receptor cells surrounded by several layers of pigment cells. There are no lenses in the ommatidia of the clam eyes. All three species of ark clam also have many pigment-cup eyes on the mantle edge. The cup eyes lack lenses, and the cavity of the cup is filled with rhabdomeric microvilli from the receptor cells. The crystalline cones in the sabellid compound eyes are powerful lenses that reduce the field of view of the receptor cells to slightly more than 10°. The lensless ommatidia ofBarbatiahave much larger fields of view (« 30°). This difference correlates with a behavioural response to much finer moving stripes in the fan worms. A comparison of compound eyes and cup eyes inBarbatiareveals a poor resolution in both, but a much higher sensitivity is estimated for the cup eyes. The tentacular eyes of fan worms and the mantle eyes of ark clams trigger protective responses: retraction into the tube and shell closure, respectively. The responses are triggered by visual motion and the eyes work as burglar alarms rather than imaging eyes. For this purpose, the compound eyes may seem to occur in affluent numbers: 240 eyes with a total of 12 000 ommatidia inSabellaand 300 eyes with a total of 39 000 ommatidia inBarbatia. The number of ommatidia that simultaneously monitors any direction in space is, on average, 43 inSabellaand 755 inBarbatia. The large number of eyes is explained as a visual strategy which provides a robust alarm system designed to reliably detect predators without causing false alarms. The literature on tentacular eyes of fan worms and mantle eyes of bivalves is reviewed, and the evolutionary origin of these independently-acquired visual organs is discussed. I suggest the possibility that hyperpolarizing photoreceptor cells (shadow detectors) evolved from chemoreceptors that were inhibited by light.

Behavioral and Physiological Responses to Emersion in Freshwater Bivalves

SYNOPSIS. Littoral lentic and shallow lotic freshwater habitats are unpredictable in periodicity and duration of shore emersion. As a result, freshwater bivalves have evolved extensive capacities to withstand prolonged emersion. Valve movement behaviors allow emersed bivalves to control rate of water loss while maintaining at least partial aerial gas exchange; these behaviors are affected by environmental variables such as temperature and relative humidity. Aerial oxygen uptake is associated directly with valve ventilatory behaviors and mantle edge exposure. Such behaviors are often phasic, indicative of oxygen “debt” payment. Lacking effective hemolymph buffer, respiratory acidosis during emersion is compensated by shell carbonate stores allowing hemolymph PCO2 to rise to levels facilitating diffusion of CO2 to the environment. During emersion, hemolymph calcium can increase four fold while Na and Cl are tightly regulated. Ammonia production ceases in emersed bivalves. It resumes on reimmersion, indicative of heavy reliance on non-protein catabolism during emersion. Some emersion adaptations of freshwater species appear to be modifications of those displayed by intertidal and estuarine bivalves, while others appear independently evolved to allow survival of the extreme emersion periods associated with life in shallow freshwaters.

A special adaptation to planktonic life in larvae of the Cassoidea (=Tonnoidea) (Gastropoda)

Living veligers of the Cassoidea have been observed to use a mantle appendage to form and resorb periostracum. Anatomical and histological examinations of a ranellid (Cymatium sp.) larva collected from the Red Sea in 1987 revealed the structure and location of the pallial appendage. The mantle edges of juvenile or adult species of the Cassoidea do not show a comparable specialization. It is demonstrated that cassoid larval conch characters are sufficient to prove the existence of a pallial appendage without anatomical confirmation. A mantle appendage is not known from teleplanic (long-living planktic) veligers of other gastropod superfamilies. In cases where the larval strategies of the latter are known they are totally different. Therefore it is suggested that the adaptation of cassoid larvae to pelagic life is unique among gastropods representing an autapomorphic character of the superfamily.

Neurotransmitters in the nervous system of Macoma balthica (Bivalvia)

The distribution of histamine-, octopamine-, gamma-aminobutyric acid- (GABA) and taurine-like immunoreactivity in the bivalve mollusc Macoma balthica was studied immunocytochemically with antisera produced in rabbits. Histamine levels in the ganglia and whole animals were also measured by high-performance liquid chromatography using a postcolumn derivatization method. Immunoreactivity for these substances, except for taurine, is found in the central nervous system of this species. The most extensive neuronal system is revealed with the antiserum against histamine. All the main ganglia contain histamine-immunoreactive cell bodies, and a dense network of nerve fibers is seen in the ganglia and nerve roots. Histamine-immunoreactive nerve fibers project to the mantle edge, lips and oesophagus. The basal part of the inhalant siphon is rich in histamine-immunoreactive fibers. Unlike histamine, octopamine- and GABA-like immunoreactivities are restricted to the central nervous system. Taurine-like immunoreactivity is not found in the nervous system of this species. In the nervous system, histamine-immunoreactive cell bodies and fibers are more numerous than those that are octopamine- and GABA-immunoreactive. The distribution of these substances in the ganglia is different. GABA-immunoreactive cells are typically smaller than most of the histamine- and octapamine-immunoreactive cells. Most GABA- and octopamine-immunoreactive cells and fibers are located in the pedal ganglion. Histamine is distributed more evenly in the ganglia and nerve roots. The biochemical measurements of histamine correlate well with the immunohistochemical findings and confirm the predominant location of the amine in the nervous tissue. These results suggest that histamine is more widespread than some other putative transmitters, and support the concept that histamine may have an important role in many physiological processes in molluscs.

Salinity tolerance of juvenile scallops ( Pecten maximus L.) at low temperature

The effects of reduced salinity on survival, filtration rate and behaviour of juvenile scallops ( Pecten maximus) were studied at 5.0°C and 9.4°C. Daily observations of mortality and behaviour, and weekly measurements of filtration were made for 30 days at the original salinity of 33 ppt, and at reduced salinities (29, 26, 23, 20 ppt, and weekly fluctuating between 27 and 29 ppt) and thereafter for a 15-day recovery period at the original salinity. The results show that there was no mortality in scallops at 9°C at salinities above 20 ppt and only low mortality at 20 ppt, while the scallops at 5°C had high mortality (> 50%) at salinities lower than 26 ppt. The filtration rate showed little variation between salinities above 20 ppt at 9°C, and between salinities at 5°C and 20 ppt at 9°C. The filtration rate in salinities over 20 ppt at 9°C was 4–5 times higher than at 5°C. The scallops responded to reduced temperature and salinity by retracting tentacles and mantle edge or closing valves. It is recommended that scallop farms in western Norway should be located in areas where salinity seldom drops below 29 ppt.

Ultrastructure and Cytochemistry of Periostracum and Mantle Edge of Biomphalaria glabrata (Gastropoda, Basommatophora)

Abstract Three layers of different electron density can be distinguished in the periostracum. Periostracal units of up to 900 nm length are merged into the outer fibrous layer and binding of gold‐labelled lectin‐WGA indicates the presence of chitin because it is labile to chitinase treatment.The periostracum is formed by the epithelia of the groove and the belt at the mantle edge. The distal and basal epithelium of the groove consists mainly of type A cells with an extended Golgi apparatus and apical vesicles. The presence of peroxidase and phenol oxidase indicates a function in tanning of the periostracum. In the proximal epithelium of the groove, type B cells with protruding apices add more material for periostracum formation. Type C cells secrete single periostracal units which are formed within single vesicles or larger vacuoles. Type D cells secrete electron‐dense vesicles which also contain WGA‐positive material.The distal cells of the belt are characterized by predominating strands of the rER while subapical vacuoles, to some of which WGA binds, dominate in the cells of the central part. In the belt, phenol oxidase and peroxidase can be localized in cisternae of the rER and the Golgi apparatus. Numerous control incubations indicate that, indeed, two different enzymes are localized.

Mantle histology, histochemistry and ultrastructure of the pearl oysterPinctada margaritifera(L.)

The edge and isthmus of the mantle of Pinctada margaritifera (Mollusc, Bivalvia) were studied using light and electron microscopy from a morphological and histochemical point of view. Six areas with several subareas were differentiated in the mantle edge. One of these areas is similar to the epithelium isthmus. Trials to elucidate the nature of the pigment responsible for the black colour of the shell and pearl indicate a melanin-like material. Possible functions of the distinctive epithelial areas in Pinctada margaritifera mantle are discussed according to available data on the secretion of organic matrix of the shell, protein selerotization and deposition of crystals in some pearl-forming molluscs. Three different epithelial areas in the outer mantle edge of Pinctada margaritifera are probably involved in the sequential processes of deposition of calcite prisms, aragonite fibres and aragonite rhombs.

Immunocytochemical localization of insulin-related peptide(s) in the central nervous system of the snail Helix aspersa Müller: involvement in growth control.

1. The presence of insulin-like substances has been demonstrated by immunocytochemistry in the central nervous system of the snail Helix aspersa. 2. The immunopositivity has been observed especially in the large perikarya of the mesocerebral green cells [the cerebral green cells (CeGC) stained in green by the alcian blue:alcian yellow technique]. 3. The removal of either the mesocerebrum or the CeGC stops the growth of the snail and induces the increase of the glycogen content in the mantle edge. 4. Our results show the existence of insulin-like material in the neurosecretory cells. Previous data having demonstrated the presence of specific binding sites to insulin in the cephalic ganglia of Helix aspersa, one may suggest that insulin could play a neuromodulatory or a neurotransmittory role in the central nervous system and might control the growth.

Isolation and partial characterization of cadmium-induced metallothionein-like proteins in Mytilus galloprovincialis

Induced cadmium-binding proteins in Mytilus galloprovincialis were isolated from digestive gland and mantle edge tissue by conventional column liquid chromatography using gel-filtration (Sephadex G-75) and anionic-exchange (diethylamino ethyl-cellulose) techniques. Isolated protein fractions were considered to be metallothionein-like proteins (MLPs) due to their high cadmium and sulphydryl content, as well as their chromatographic behaviour and spectral characteristics. Two negatively charged MLP components (MLP-I and MLP-II) were separated from digestive gland, both possessing a molar mass of 12.6 kDa as determined by electrophoresis. The electrophoretic profile of mantle edge MLP showed another strongly pronounced band of 26 kDa in addition to one at 12.6 kDa, indicating the occurrence of a predominantly dimeric form in that tissue. The sulphydryl to cadmium ratio, determined by electrochemical and spectrophotometric methods, in addition to flameless atomic absorption spectrophotometry (AAS), was in the range between 2.1 and 2.5 in the highly purified, electrophoretically homogeneous MLP-II component from the digestive gland of M. galloprovincialis. This is considerably lower than the well-defined binding stoichiometry of mammalian type metallothionen. This observed lower cysteine to cadmium ratio may conceivably be related to a specific coordination geometry, presumably implicating mixed ligand complexation of metal-binding sites in MLPs of M. galloprovincialis.

Embryonic development of the shell in biomphalaria glabrata (Say).

During embryogenesis of the fresh water snail Biomphalaria glabrata (Say) (Pulmonata, Basommatophora) shell formation has been studied by light and electron microscopical techniques. The shell field invagination (SFI), the secretion of the first shell layers, the development of the shell-forming mantle edge gland and spindle formation have been investigated. During embryonic development at 28 degrees C environmental temperature, the shell field invaginates after 35 h. After 40 h the SFI is closed apically by cellular protrusions and scale-like precursors of the periostracum. The first electron translucent layer of the periostracum stems from electron dense vesicles of the cells which lie at the opening of the SFI. A second electron dense layer appears some hours afterwards. When the shell appears birefringent in the polarizing microscope (45 h of development) calcium can be detected in it using energy dispersive x-ray analysis. As calcification occurs the intercrystalline matrix appears under the periostracum and the SFI begins to open. In embryos of 60 h the mantle cavity appears at the left caudal side. When the mantle edge groove develops (65 h of development) lamellate units are added to the outer layer of the periostracum, but no distinct lamellar layer is formed in B. glabrata. In addition to the lamellar cell and the periostracum cell, a secretory cell can be observed in the developing groove. After 65 h of development, spindle formation starts and the shell begins to coil in a left hand spiral. After 5 days of development the embryos are ready to leave the egg capsules.

Mechanical constraints on aperture form in gastropods.

Gastropod apertures reflect expanded states of their mantle edge under variable boundary conditions. The apertures are divided into two groups: apertures without distinct overlap zones (e.g., whorl overlap) and those with overlap zones. Each group follows a unique morphological rule. Apertures without overlap zones are generally circular in outline. Apertures with overlap zones are either elongated perpendicularly to the overlap zone or inflated abapically. Moreover, the latter abapically inflated apertures are generally accompanied by a straight section anterior to the overlap zone along the columellar axis (columellar part). Numerical analysis of an elastic double membrane tube whose main frame simulates the gastropod mantle indicates that these morphological rules are the products of mantle edge expansion under the condition that the head-foot mass presses against the mantle edge in both the overlap zone and the columellar part. The mantle edge in these two zones is thus in a completely or partly fixed boundary condition at the moment of shell growth. The rest of the mantle edge is free to expand either symmetrically or asymmetrically. It is hypothesized that the head-foot mass is a driving force for regulating the pattern of shell coiling and apertural shape.

New species, anatomy, and systematic position of the hydrothermal vent and hydrocarbon seep gastropod family Provannidae fam.n. (Caenogastropoda)

The anatomy of the hydrothermal vent gastropod Provanna is described. It is shown to be a primitive neotaenioglossan with mainly plesiomorphic features in all systems, including open pallial gonoducts, epiathroid nervous system with accessory pedal ganglia and a circulatory system where a considerable portion of the venous blood from the coelomic spaces enters the pallial skirt. Apomorphic features include the possession of an anterior notch, or short canal in the shell (and mantle edge), an annulated sensory pallial tentacle, paraspermatozoa modificd as nurse cells. multiple seminal receptacles, a posterior bursa copulatrix, and a renal oviduct with three distinct regions. the middle one expanded. Comparisons are madc with Abyssochrysos, a genus assumed to be a relict member of the Loxonematoidea, which appears to be the closest known relative. A new family. Provannidae fam.n., is created and tentatively included in the Loxonematoidea. The following new specics are described: Provanna segonzaci sp.n. (from hydrothermal vents at the Fiji Back Arc), P. laevis sp.n. (from hydrothermal seeps in the Gulf of California), P. sculpta sp.n. and P. admetoides sp.n. (from hydrocarbon seeps in the Gulf of Mexico). New records are added for previously described species of Provanna.

Finite element analysis of a double membrane tube (DMS-tube) and its implication for gastropod shell morphology.

Molluscan shells, including those of Gastropoda, are formed by accretionary growth at the mantle edge. The mantle is a thin membrane of skirt-like shape, which extends minutely beyond the aperture, and its edge adds a shell increment to the aperture margin so that each increment copies a configuration of the mantle edge at that time. Thus, regulation of shell morphogeny is almost equivalent to the factors which control the mantle form at the moment of shell growth. Form of the mantle skirt is considered to be kept in a state of balance between the force of its internal stress and forces acting on it such as fluid pressure or muscle contraction. The expansion behavior of the mantle skirt has been numerically analyzed by using an elastic model (DMS-tube), which represents the fundamental structure of the mantle tissue as a double membrane structure with internal springs (DMS). Four characteristic expansion patterns of the DMS-tube have been detected: (1) general outward expansion; (2) developing a ridge-like fold on an initial longitudinal protrusion of the tube edge; (3) drastic shift of the expanded state from a uniformly curved to an elliptical shape in outline, owing to the existence of a fixed boundary condition on the tube wall; and (4) constricted protrusion on the open region of the shell wall surrounding the DMS-tube. These results have the potential for answering the following questions relating to the morphogenesis of gastropod shells. How does the mantle skirt usually make contact with the inner surface of the shell wall so as to ensure continuous accretion of shell materials to the aperture margin? What is the cause of spiral ridges? Why do open coiling or minimally overlapping shells have generally circular apertures, while shells with apertures overlapped by whorls have non-uniformly curved apertural lips? What is the cause of long closed spines and why do they always appear on spiral ridges?

The anatomy of some new archaeogastropod limpets (Order Patellogastropoda, Suborder Lepetopsina) from hydrothermal vents

The anatomy of one species of neolepetopsid limpet, Eulepetopsis vitrea (Order Patellogastropoda, Suborder Lepetopsina), is described, and this is followed by comments on differences shown by four other members of the Suborder, Neolepetopsis occulta, N. densata, N. gordensis and Paralepetopsis fioridensis.These limpets possess features linking them directly with limpets from other habitats, in this case with patellogastropods. Shared external features relate to the shallow pallial cavity with no gill; the single fold of the mantle edge, which is sensory, glandular, and has a respiratory function; in the gut the presence of inner as well as outer lips, with a strongly arched dorsal jaw associated with the former; the absence of an epipodium; and the cavity of the protoconch sealed from that of the teleoconch by a septum. The relationship displayed by internal anatomy is even more striking: the docoglossate radula and licker; the oesophageal glands forming a series of pouches, each with its own opening to the oesophagus; the stomach a simple ciliated sac lacking gastric shield, sorting area, and caecum; the enlarged initial part of the intestine; the orientation of the chambers of the heart, which is not traversed by the rectum; the lack of haemocyanin; the opening of the gonad directly to the base of the papilla of the right kidney; the absence of secondary sexual structures; the small left kidney displaying characters of a nephridial gland; and the degree of concentration of the main ganglia and the arrangement of the visceral loop. This aggregate of characters shows that the neolepetopsids cannot be separated from patellogastropods.The radula of the neolepetopsid differs from that of other patellogastropods in its unmineralized and articulating teeth and in the presence of a rachidian: the first feature appears to be a derived character and the other two ancestral. These radular differences contrast with the anatomical homogeneity exhibited not only here but throughout the patellogastropods. Such anatomical differences as do occur are most easily explained as mosaic evolution.

Behavioral and Metabolic Responses to Emersion and Subsequent Reimmersion in the Freshwater Bivalve, Corbicula fluminea.

When exposed to air, the freshwater bivalve, Corbicula fluminea, displayed valve movement behaviors, such as mantle edge exposure, wider gaping "ventilatory" response, and an escape or "burrowing" response. The proportion of the emersion period spent in these behaviors, relative to valve closure, increased with decreasing temperature. Emersion at 35°C inhibited valve movement behaviors, whereas emersion in a nitrogen atmosphere stimulated ventilatory activity. High rates of aerial oxygen uptake (Mo2) were associated with initial valve opening and ventilatory behaviors, and lower Mo2 occurred during bouts of mantle edge exposure. Heart rate was affected by temperature, but not by mantle edge exposure. Heart rate increased during burrowing and ventilatory behaviors suggesting a hydraulic function for hemolymph. Emersed C. fluminea had short bursts of heat production followed by longer periods of lower heat flux when measured by direct calorimetry. The mean heat production rate was 1.11 mW (g dry tissue)-1, significantly higher than the mean value for clams exposed in a nitrogen atmosphere, 0.50 mW (g dry tissue)-1. On reimmersion, C. fluminea showed no significant "oxygen debt" until after three days aerial exposure. The bursts of activity, while emersed, may be the result of periodic renewal of oxygen stores followed by immediate oxygen use.

The anatomy of some new archaeogastropod limpets (Superfamily Peltospiracea) from hydrothermal vents

The anatomy is described of seven new species of limpet from hydrothermal vents in five new genera in the new family Peltospiridae, new superfamily Peltospiracea (McLean, 1989). Distinguishing external features are: (1) the tapering snout; (2) no eyes; (3) epipodium with tentacles variously modified; (4) deep mantle cavity; (5) single left bilamellate gill with pectiniform skeleton; (6) separate sexes; (7) no copulatory organ; (8) mantle edge with two folds, the outer secreting the shell with an inturned rim of periostracum, the inner sensory and differing in detailed structure of the secreting areas.Limpet form is attained by the anterior migration of the posterior viscera into the mantle skirt on the right side. On the left is the single kidney, with monotocardian characteristics, followed posteriorly by the auricle and then the ventricle (not traversed by the rectum), which marks the posterior limit of the mantle cavity. The auricle receives blood from a pallial as well as a ctenidial circulation. There is no right kidney but a pallial excretory organ opens right of the rectum.The radula is rhipidoglossate. The alimentary canal resembles that of a primitive prosobranch though with an odontophore indicating more powerful action, a subradular organ protrusible through the mouth and held in position by the tapering snout, and paired oesophageal pouches providing the most voluminous cavity of the body.The gonadial duct acts as a vesicula seminalis in the male, and in the female opens into the kidney, the external opening of which is, in this sex, urinogenital. A second, receptacular duct, pallial in origin, connects with the ovary, opening to the mantle cavity near the anterior limit of the shell muscle and receiving seminal fluid emitted from the pallial vas deferens. Sperm are discharged directly into the ovarian duct, viable ones are stored and effete ones digested. The anatomy indicates that fertilization is internal. A levator muscle regulates the position of the openings of the gonadial and receptacular ducts within the ovary. It originates alongside the median margin of the right limb of the horseshoe‐shaped shell muscle.Relationships with other vent limpets are discussed.

Cavitatus D.M. Williams, nov. gen.: A new genus of fossil diatom (Bacillriophyta) based on Synedra jouseana Sheshukova-Poretskaya

A morphological investigation of the marine, Oligocene to Miocene fossil Synedra jouseana has been undertaken. This species cannot remain in the genus Synedra and appears to be similar to Thalassionema and Thalassiothrix. However, it differs from both by the possession of deep longitudinal valvar canals that penetrate the mantle edge and a distinctive furrowed sternum. Hence it is placed in a new genus. Its relationships within the araphid diatoms are briefly discussed.

Variations of somatostatin-like immunoreactivity in the circumoesophageal ganglia, the hepatopancreas, the mantle edge, and the hemolymph of shell-repairing snails ( Helix aspersa)

Immunocytology and radioimmunoassays demonstrate the presence of immunoreactive somatostatin-like (IR-SOM-LI) material in the tissues of young or adult snails Helix aspersa bred under short or long day in controlled artificial conditions. Neurosecretory cells in the circumoesophageal ganglia and in the digestive gland, small fibers in the hepatopancreas, and small granules in the mantle epithelial cells are immunoreactive toward antisomatostatin 14. In all experimented animals shell fractures induce variations of the IR-SOM-LI concentrations in all assayed tissues whatever the lighting conditions were underwent. These findings support the hypothesis that in Helix one or more substances related to the vertebrate tetradecapeptide is (are) involved in the repair processes but that the storage and the metabolism may be different during the biological cycle of the snails. These results are compared with those previously published using different gastropods and different methods.

Central and peripheral expression of genes coding for egg-laying inducing and insulin-related peptides in a snail.

Egg laying in the hermaphrodite freshwater snail Lymnaea stagnalis is a highly complex activity, including a series of internal activities (ovulation, egg and egg mass formation) which are closely correlated to a pattern of behaviours (alteration of locomotion and feeding, specific postures, oviposition). In this snail egg laying is induced by the neuroendocrine caudodorsal cells (CDCs), consisting of two homogeneous clusters at a total of 100 neurons. At egg laying these neurons release their products during a 60 min period of firing. The genes coding for these products have been cloned and characterized. There are two genes, CDCH-I and -II. Each gene codes for 12 peptides; one of these is the ovulation hormone (CDCH). The genes display over 90% homology. The most striking difference is a 17 bp deletion near the carboxy-terminal region. With immunocytochemistry and in situ hybridization both CDCH genes appeared to be expressed in the CDC and in paired groups of ectopic CDC-like neurons in the pleural ganglia, while a group of small neurons in the cerebral ganglia expresses the CDCH-I gene only. In addition, a widespread expression of the CDCH genes has been demonstrated in peripheral tissues. In the female part of the reproductive tract neurons were found to express the CDCH-I gene. In the male part of the tract exocrine secretory cells express the CDCH-I or -II gene. The gene products are secreted into the male tract and transferred to the female partner during copulation. Finally, sensory neurons in the head skin and mantle edge were found to express the CDCH-I gene. The presence of insulin-related peptides has been demonstrated in the brain as well as the digestive system of Lymnaea. The brain insulin-related peptides are produced in 4 groups of 50 giant neurons each (Light green cells, LGC). These neurons are involved in various physiological activities, related to body growth and glycogen metabolism. The major gene products expressed in the LGC have been cloned and characterized. It appeared that the predicted proteins represent three types of insulin-related molecules (MIP, molluscan insulin-related peptide). In these MIPs, those elements important in the determination of the tertiary structure, have been conserved. The MIP of the digestive system has been characterized up to now only at the peptide level. The snail gut MIP is more hydrophobic compared to bovine insulin. Cells containing MIP have been identified immunocytochemically in the gut epithelium.